Levamisole, a common cutting agent in cocaine, made the news recently for its apparent skin-destroying properties – but there's a lot more to the substance than that.

A case study from the 'British Medical Journal' of a woman whose skin and flesh is rotting due to the presence of levamisole in the cocaine she had been taking. Photo courtesy BMJ

Corrupted cocaine sold in Britain is making people's skin rot. Or so we were told last week, when a series of reports warned of the "flesh eating" cocaine causing people to suffer from a rare blood disorder that makes their flesh decompose and their ears go black. The stories came with images from a gruesome case study in the British Medical Journal, of a woman covered in dark blotches and open sores, looking like something out of a medieval physician's casebook.

Newspapers revealed the culprit: levamisole, a cattle de-worming drug found in "80 percent of cocaine" in the UK. The message being: do a bit of a gear and you'll lose all your skin.

Of course, where there are drugs, a scare story is never far behind – and the first myth to blow away here is that levamisole is any great danger to the general cocaine-snorting public. Despite the hype, the chances of cocaine giving you a blood disorder or rotting your skin are incredibly remote. Unless, that is, you're from northern Finland (which I'll get to later).

Levamisole has, over the last decade, become a major cutting agent in the world's cocaine supplies. Depending on where you live, between 40 to 90 percent of cocaine contains the drug. The British government says around 80 percent of seized cocaine shipments in 2014 contained levamisole. In Spain, a 2012 study found the drug in 57 percent of cocaine, and in Denmark in the same year it was in 90 percent of samples. In Holland, the figure is 60 percent, and in the US the DEA puts it at 73 percent.

While the substance might be found frequently, that doesn't mean cocaine is packed with the stuff. Cocaine purity research carried out by Lana Brockbals at drug identification firm TICTAC, seen exclusively by VICE, found that out of 106 samples of cocaine from an unnamed British festival last year, 83 contained traces of the de-wormer. However, the average concentration of levamisole in each wrap was just over five percent, with most samples containing between 1.5 and five percent of levamisole.

Tests on 5,000 street cocaine samples in the Netherlands between 2011 and 2014 found an average concentration of nine percent. In Spain last year, concentration was found to be, on average, 11.9 percent. The DEA says levamisole takes up nine percent of the average American bag of cocaine. An analysis last year of 103 random cocaine samples from around the world, conducted by the Energy Control drug testing service, found that the average concentration was 11 percent.

So does snorting cocaine that contains five, 10 or even 20 percent levamisole warrant the media hype? After all, there are up to an estimated 21 million cocaine users on the planet – you'd expect the hospitals to be rammed with people losing all their skin. But they're not.

I spoke to Dr Lindy-Anne Korswagen, one of the authors of the BMJ study mentioned in all the papers last week, and a doctor at Sint Franciscus Gasthuis Hospital in Rotterdam. "Given the fact that many people use cocaine, of which large percentages are adulterated with levamisole, our case is rare," she said. "The risk of side effects such as agranulocytosis or levamisole-induced vasculopathy with skin ulcers and serious organ damage is small. Between 2011 and 2014, there were 210 cases reported worldwide, of which three have died."

Dr Korswagen did warn that there may be undiagnosed cases out there.

(Photo by Andoni Lubaki)

The authors of a similar case study (someone suffering from a levamisole-induced skin disease) published in a US medical journal in 2013 said most victims they had come across were heavy cocaine users. "Many of these affected individuals are chronic, habitual cocaine users, suggesting a large cumulative exposure to cocaine and, by association, levamisole, possibly over an extended period of time."

Toxicologist Dr Robert Hoffman, an expert in levamisole from the New York University Langone Medical Center, told me the amount of the drug found in the average bag of cocaine "is probably too low" to affect most users, and that when levamisole was used as a legitimate pharmaceutical in medical trials, most patients tolerated full therapeutic doses without a problem. "Let's say the typical dose of cocaine might be 100mg, so there could be 10mg of levamisole in each dose of cocaine used. Currently, there are still trials where levamisole is used and a dose might be on the order of 150mg over a day. To get that much levamisole, you would have to use a lot of cocaine," he said. "So yes, to an extent, the low concentration is somewhat protective in that the total daily dose will be low."

But it turns out it may not just be about dose; Dr Hoffman told me the evidence points to some people having a genetic vulnerability to the toxic effects of the drug. "The literature suggests that some patients have a unique genetic predisposition that increases their risk of toxicity," he said. "There is always some consideration for dose, but it is a combination of dose plus susceptibility that sets the risk. Luckily for cocaine users, the known responsible genetic abnormality is very uncommon."

The gene in question, HLA-B27, is present in about eight percent of caucasians, four percent of North Africans, two to nine percent of Chinese and 0.1 to 0.5 percent of Japanese. Oddly, in Lapland in northern Finland, a quarter of people have the gene.

That levamisole is far less of a threat to human health than the media is making out is really no surprise. In such a hugely profitable business as the cocaine trade, you're not going to do all that well making a product that turns your global customer base into a mass of sick or dying invalids – Imperial Tobacco and Philip Morris excluded. Instead, the use of a cattle de-wormer in cocaine is an indicator of how astute the cocaine cartels really are, because they appear to have unearthed the most efficient cocaine-cutting agent of all time.

A report due to be published later this year by a specialist unit dedicated to monitoring the chemicals used to produce cocaine, attached to the UN Office on Drugs and Crime (UNODC), found the use of levamisole to be far from anomalous. It is a strategy based on a firm business and scientific footing.

Conducted by PRELAC (Prevention of the Diversion of Chemical Precursor Substances of Drugs in the Latin America and the Caribbean Countries), the study reveals Colombian firms were the first to start using levamisole a decade ago. Now it's also used by cartels in Peru and Bolivia as the "cut" of preference for bulking out cocaine before it's exported. In cocaine, levamisole is usually mixed with two other chemicals, such as diltiazem, phenacetin, hydroxyzine and caffeine. For the US and European markets, cocaine is cut 20 percent. If it's going to other countries in South America, such as Brazil, it can be cut to as much as 50 percent.

The authors of the report, "Dynamics of chemical use in the production of cocaine in the Andean Region", say there are a number of reasons why levamisole has become the number one cut. It's easy to mix with cocaine, has a similar "fish scale" appearance to high quality cocaine flake and gives the impression of having a greater volume than it actually possesses. It also gives a false positive in street tests for cocaine, so bulk buyers are not able to spot the cocaine has been cut, and is relatively cheap and easily available in bulk from cities across the Andean countries. According to an expert working for the UNODC in Colombia, the drug is regularly purchased at £32 per kilo in Bogota, Cali and Medellin, compared to £1,500 for a kilo of cocaine.

According to the UNODC, levamisole is incorporated into cocaine hydrochloride in two stages of the process: before converting cocaine base to cocaine hydrochloride, and later, when the hydrochloride has already been obtained but has not yet dried. So it's in almost everyone's cocaine, even the super rich – although I'd guess there are a few mega-mansions in Colombia and Miami where the cocaine is as pure as it comes.

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But the game changer – an asset of levamisole of which cartel chemists will be fully aware – is its ability to potentiate the action of cocaine in the body. A metabolite of levamisole called aminorex has amphetamine-like properties, and a growing body of research is beginning to suggest what the Colombian chemists may have known all along: cocaine mixed with levamisole creates an additional high when it's snorted.

"[The cocaine cartels] have extensive financial networks, and we must assume that this drug adds to the potency or addicting qualities of cocaine in a way we have yet to fully determine," said Dr Hoffman. "They have access to animal labs and thousands of human subjects, and therefore the addition of levamisole to cocaine is undergoing more testing than most approved drugs."

These days, cartel chemists are a very different breed to the TV depiction of a guy in a baseball cap stirring a bucket in the middle of the Amazon rainforest. "It's a mistake to think Colombian cocaine producers are peasants in a jungle lab," says Mike Power, a journalist and author who has investigated the Colombian cocaine trade. He told me the much-filmed rural farmers (cocaleros) are only part of a big supply line from farmyard to nostril, involving chemistry, airplanes, murder and corruption.

"It would be astonishing if the narco-cartels didn't know about the emerging evidence around the stimulant effects of levamisole," Power said. "Four years ago in Colombia, I saw how the crystallisation [of the paste] process was moving from the jungles to underground urban labs, in well guarded apartment blocks. This is a complex science. If they can increase their profits by 10 percent by including an active cut that ticks all the boxes, then it's a no-brainer. And because most of it is being added at end of the process, before export, we know it's being facilitated by people at the high end of the trade. They know exactly what they are doing."

But, as Power says, the end result for many cocaine users is that while the powder might be white, it's anything but pure. "The fact is, if you've been using coke," he said, "you've been snorting cattle de-wormer for years now, and you're paying through the nose for the privilege."